In recent years, new fine processing technologies have been developed as the integration degree of semiconductor integrated circuits (hereinafter referred to as LSIs) and the performance thereof have been becoming high. Chemical mechanical polishing (hereinafter referred to as CMP) is also one of the technologies, and is a technique used frequently in the process of producing LSIs, in particular, in the planarization of an interlayer dielectric layer, the formation of metallic plugs, or the formation of embedded interconnections in a multilayer interconnection forming step. This technique is disclosed in, for example, the specification of U.S. Pat. No. 4,944,836.
In order to make the performance of LSIs high, attempts of making use of copper or copper alloy as an electroconductive material which is to be a wiring material have been recently made. However, copper or copper alloy is not easily subjected to fine processing based on dry etching, which is frequently used to form conventional aluminum alloy wiring. Thus, the so-called damascene process is mainly adopted, which is a process of depositing a copper or copper alloy thin film on an insulating film in which grooves are beforehand made, so as to embed the film therein, and then removing the thin film in any region other than the groove regions by CMP to form embedded wiring. This technique is disclosed in, for example, JP-A-2-278822.
An ordinary method of CMP for polishing a metal for wiring regions, such as copper or copper alloy, is a method of causing a polishing pad to attach onto a circular polishing table (platen), impregnating the surface of the polishing pad with a metal polishing slurry, pushing a metal-film-formed surface of a substrate against it, and rotating the polishing table in the state that a predetermined pressure (hereinafter referred to as a polishing pressure) is applied thereto from the rear surface of the polishing pad, thereby removing convex portions of the metallic film by effect of mechanical friction between the polishing slurry and the metallic film convex portions.
A metal polishing slurry used for CMP is generally composed of an oxidizing agent, abrasive grains, and water. If necessary, a metal-oxide-dissolving agent, a metal anticorrosive agent, and others are added thereto. The surface of a metallic film is first oxidized with the oxidizing agent to form an oxide layer, and the oxide layer is ground away with the abrasive grains. This is considered to be a basic mechanism. The oxide layer in concave regions of the metallic film surface does not contact the polishing pad very much; thus, the grinding-away effect of the abrasive grains is not given thereto. Therefore, with the advance of CMP, the metallic film convex regions are removed so that the substrate surface is planarized. Details thereof are disclosed in Journal of Electrochemical Society, Vol. 138, No. 11 (1991), 3460-3464.
It is mentioned that an effective method for making the polishing rate of CMP high is the addition of a metal-oxide-dissolving agent. This can be interpreted as follows: when grains of a metal oxide ground away with the abrasive grains are dissolved into the polishing slurry, the grinding-away effect of the abrasive grains increases. The addition of the metal-oxide-dissolving agent causes an improvement in the polishing rate of CMP; however, when an oxide layer in concave regions of a metallic film surface is also dissolved so that the metallic film surface is made naked, the metallic film surface is further oxidized with the oxidizer. When this is repeated, the dissolution of the metallic film concave regions unfavorably advances. As a result, there is generated a phenomenon that a central region of the surface of metallic wiring embedded after the polishing is depressed into a dish form (hereinafter, the phenomenon will be referred to as “dishing”). Thus, the planarizing effect is damaged.
In order to prevent this, a metal anticorrosive agent is further added to the metal polishing slurry. The metal anticorrosive agent is an agent for forming a protective film on the oxide layer on the metallic film surface to prevent the oxide layer from being etched.
This protective film can easily be ground away with the abrasive grains. It is desired that the protective film does not cause a fall in the polishing rate of CMP.
In order to restrain the dishing or etching of a metallic film to form LSI wiring high in reliability, suggested is a method using a metal polishing slurry containing a metal-oxide-dissolving agent made of an aminoacetic acid, such as glycine, or amidesulfuric acid, and benzotriazole as a metal anticorrosive agent. This technique is described in, for example, JP-A-8-83780.
Beneath a metal for wiring regions, such as copper or copper alloy, a layer made of a conductor such as tantalum or a tantalum compound is formed as a barrier layer in order to prevent the metal from diffusing into the interlayer dielectric layer, or improve the adhesive property of the metal onto the interlayer dielectric layer. It is therefore necessary to make use of CMP to remove the barrier layer naked in any region other than the wiring regions into which the wiring region metal such as copper or copper alloy is to be embedded. However, the conductor of the barrier layer is higher in hardness than copper or copper alloy; therefore, a combination of polishing materials for copper or copper alloy does not give a sufficient polishing rate and further makes the flatness and smoothness of the polished surface poor in many cases. Thus, a two-stage polishing method is being investigated which is composed of a first CMP polishing step for polishing the wiring region metal such as copper or copper alloy, and a second CMP polishing step for polishing the barrier layer.
The metal polishing slurry used in the second CMP polishing step for polishing the barrier layer may be required to attain ability to polish a silicon-coating film or an organic polymer film, which is an interlayer dielectric layer in order to promote the planarization of the polished surface. In order to improve the polishing rate of the interlayer dielectric layer, suggested is a method of enlarging the particle diameter of the abrasive grains contained in the metal polishing slurry to perform polishing. However, the method has a problem that scratches are generated in the surface polished therewith, thereby causing electric characteristic insufficiency. There is also caused a problem that such electric characteristic insufficiency is generated by insufficient washing after the CMP.